Methyltertiarybutyl ether (MTBE) is well-known as a high octane blending component for motor fuels. The well-known reaction of methanol (MeOH) and isobutylene, using an appropriate catalyst, such as Amberlyst 15, has been practiced to produce MTBE. Reference is had to U.S. Pat. Nos. 4,071,567; 3,979,461; 3,135,807; 3,846,088; among many others.
HF catalytic alkylation of isobutane with olefins, such as propylene and/or butylenes, is also a well-known process for producing high octane motor fuel. In HF alkylation it is also known that too much water in HF catalyst can adversely affect the alkylation operation, including presenting problems of equipment corrosion. In addition, methanol is not wanted to be present in HF alkylation since methanol uses isobutane in its reaction therewith to produce undesired low octane, high volatility five carbon-atom hydrocarbons and water, the water undesirably diluting the HF catalyst.
Since there is some unreacted methanol and there is some unreacted isobutylene in the MTBE reactor effluent, it is desired to recover these components and to recycle the methanol, preferably, back to the MTBE reaction; and to recover the unreacted isobutylene (along with isobutane and straight chain butylenes, which hydrocarbons are present in the feed to MTBE and act as desired diluents in the MTBE reaction) and charge this recovered isobutylene, freed from methanol, to the HF alkylation.
It is desired that no methanol be yielded, and thereby lost, in the MTBE product. It is desired that substantially no water and no methanol be charged to the HF alkylation.
This invention presents a system: to produce MTBE from methanol and isobutylene with the MTBE being recovered free of methanol and water; to recover methanol and unreacted hydrocarbons; to separate a water and methanol phase from the unreacted hydrocarbons; to water-wash the unreacted hydrocarbons to remove the last traces of methanol therefrom; and to dry these water-washed hydrocarbons prior to charging the methanol-free, water-free hydrocarbons to HF alkylation; to fractionate the water-methanol phase, above-referred-to, to recover substantially pure methanol which can be recycled to MTBE manufacture; and to use the water separated from the methanol as at least part of the water used in the water-wash step, above-referred-to.